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Thursday, July 22, 2010

More on the B2031P and diffraction

I also wanted to test my diffraction theory with the ports next to the tweeter. So I got some cotton balls from the "stuff" drawer and filled the front of those ports with white cotton balls! Well, the results are something to see. The top polar and impulse graph are prior to port stuffing. The next are after the cotton balls were installed. Now I'd say it doesn't look like the woofer break up was any problem.

91 comments:

Hi - really interesting posts so thank you very much for those! I'm currently considering an upgrade to my home studio speakers from old JBL Contorl 1s to eith the Behringer 1030a or the equivalent KRKs. Would you have a moment to spare some advice for me? Money is not really an issue (but obviously I wouldn't mind saving some!) but the Behringers do seem good value for money. Many thanks, Chris (chris_evans1973@hotmail.com)

I wish I knew how your old JBLs performed. Without that info it's hard to make a recommendation. I will say that the KRK are not as good as the Behringers(that comment would make a few people gasp!). The 1030s are shockingly revealing. I've always wanted to hear/measure the 1031A... Should be a fairly ideal speaker provided the QC is good. Good luck.

how deep and how densely did you stuff the cotton in? was the idea just to level it with the baffle so that there are no edges to diffract from? do you think foam felt strips on the sides/edges of the ports could be (as) effective?

The original idea was just to absorb the wave coming off the tweeter. I'm planning on doing another experiment with a flat baffle. I'd guess that placing strips beside the port would help, but I'd also guess it would be to a lesser degree. I'd be interested in those results as well and will place it on my list of experiments. Thanks for the idea. Next time I do something with the one I have left, I'll do that too.

I was wondering about one idea for the diffraction issue. What if one were to take thin foam piece the size of baffle, cut out portions such that waveguide, tweeter and woofer is exposed and put that on the baffle. Also stuff some foam inside the ports. That would make it almost like 1031a. Do you think that would help ? Hopefully foam absorbs and doesn't diffract the sound....If that does away with diffraction and makes sound smooth, one may have better speaker than 1031a as 2031a has better pattern control and a lower crossover as well....

The foam would have to be carved so that it would have ridges perpendicular to the baffle. Wool felt should be more effective. I've been doing a fair amount of fine woodworking lately. I actually want to rebuild the one B2031P I have left. That will still be a while though. I so want to get back into this hobby. I just set up a home theater for my GF and now have the Mackies as my gag rag system. It's a blessed life. The B2031p is her center channel--it already works great there. When I rebuild it, the ports will be in the back.

Agree, foam was just an example, many other materials can be explored.But a sealed 2031 with no diffraction should be amazing...

I have one more idea which I came up with recently which though pricing wise would be higher than something like 2031A but would end up mimicking genelec 8260 or a TAD compact referenceBasically this involves using 2 KEF Q300 bookshelfs (6.5" coax) and keeping them each on top of a NHT super 8 . the super 8s can easily go upto 200 Hz so Q300 will cross to super 8 at 200 Hz . They will also be kept inverted on super 8 for closer CTC. This should be pretty close to 8260 or the TAD compact ref . And coax would behave as a waveguide better due to reduced excursion. And horizontal and vertical dispersion is no worry here...Although a pricey combination but maybe a very good one esp for nearfield [ my core objective :) ]

I was actually thinking about making the B2031P's baffle shape more similar to the shape of the plastic WG/woofer frame. I really want to do large round overs as well. It's a lot of money and work for a little sonic improvement though. However it would make a lot nicer looking speaker! It almost seems like chasing better sound than the Primus or B2031 is a high price to pay for a small (if any) reward. Listening to my ADAM Artist 5 vs. a Primus/B1031P system shows a definite performance improvement in the former, but the price difference is definitely bigger than the performance difference. The bigger difference is actually in the bass--room calibration. 4 subs vs. 2, Audyssey vs Yamaha's calibration, and a better damped vs. a less damped room.

Makes me feel like I must have been crazy to shoot for better than one if these lower cost options. That said, the 4 subs seem worth it in the long run.

I'm not saying the midrange and treble don't seem better with the ADAMs, because they do, but it was a couple thousand dollars vs. a couple hundred. The ADAMs also look a lot nicer! My Primus look pretty ugly IMO and are best with the grill left on most of the time. The ADAM look badass with the grills off. I only leave them on for protection and take them off every time I listen to them. The silver/grey look of the Primus does look low rent. The cheap pioneer look better to my eye than the Primus, but I also think they don't sound as good. If my Primus had zero grey, they'd look good enough for me. Still I love the gloss black ADAM.

For sound though, the difference is there, but it's not really enough for 5-6X the price especially considering home theater use and the fact that the floor standing Primus have less need for a sub.

Oh, one other thing: perhaps some packing tape over the B2031Ps ports would do the trick. You would probably still need to pack the ports tightly with some wool felt or something. The black wool felt I have in mine looks a million times better than the cotton balls and performs the same.

But then that would mean possible crossover changes isn't it ?Which is why I just thought of "improving" on current baffle shape ?

and yes I do expect the KEF+NHT setup to be good, but I have the same worry which you mentioned. How good will it be, esp for additional amount spent over a well modified 2030A/2031A. Thats an very very imp question :)

Btw the new JBL LSR305 has promising measurements and is quite popular as well - see here http://www.soundandrecording.musikmachen.de/Magazine/SOUND-RECORDING/2014/5/JBL-LSR-305-308-Nahfeldmonitore-Testbericht

And you can download for adam artistshttp://www.soundandrecording.musikmachen.de/Magazine/SOUND-RECORDING/2011/9/Testbericht-ADAM-ARTist-3-und-5-Studiomonitore

Btw now I am bit hesitant to about larger 2-way monitors and now understand the worry related to vertical dispersion [which you mentioned multiple times:) ]Thats apparent in the larger LSR308 as well in the above link.

So 6.5" looks like max to go for, so if Behringer may go for 2030A (with baffle modifications )

Long back ago I think wMax had shared 2030p measurements, the links don't exist now. ( in some posts where you had posted too)Do you remember if they were better/same/worse than 2031p.The 2030a has 2khz crossover ( same as 2031) and a 0.75" tweeter. Should have wider dispersion than 2031....

You can definitely hear high(ish) distortion on test tones. That tells me I don't want it--just to be safe. It's really necessary to know what output level the measurement was made--every speaker has its limits.

Right now at least one night a week I go to dance party level on one of my sound systems. I actually prefer a higher crossover F. I don't know if it is just my OCD or what, but things seem cleaner that way and it certainly doesn't effect imaging much if any at all.

Can't believe I just said that--me of all people. If I didn't have my ADAM/Canton/Marantz system, the quest for the ultimate system would still be burning in my soul. Right now I'm listening to FM with simulated SS and loving it! I would have thought that impossible 1 year ago.

True, though only advantage I see ( if I can fit them on desk and listen on tweeter level) is I need not bother buying a sub, or maybe delay that for much long time. Based on the FR on the PE post, they go very low and cleanly... only thing remains is diffraction correction which we discussed earlier (true even for 2030 though)

Do blog if you have any updates with baffle experiments. You tried the simple tape over ports ? Or bung instead of cotton...Then measuring the F3 will let know if sub is still must (sub will good though)

I think it would be a bad idea to place any broad dispersion speaker near a wall unless you were going to place it in a wall. The VERs will color the sound. I have theories on that, but they have yet to be adequately tested.

I guess Behringer went with front ports so it can be soffit mounted. But the passives would have incorporated the bsc, so i guess crossover would have to be reworked to put 2031p behind screen (assuming its side wall to side wall)

I'm not really sure which of those is better sounding. I'd say the Primus if you didn't want to modify the B2031. The thing I really like about the Primus is that it is a floor stander. It eliminates the stand and just makes a more stable and lower cost speaker option. If you have kids and dogs it becomes much better! My biggest gripe with the Primus is how they look with the grill off.

Again about HT, do you see an advantage of having large mains so that one can cross a sub at 60Hz or below or one can safely cross at 80-100z (in a medium 22' x 14' room). If the latter, one can go with wall mounted 5.25-6.5" speakers .And spend more money on 3-4 12" subs [ primus 363 at 99$ is an exception :) ]

Also you indicated earlier that the primus PC351 MTM being a promising option. Whats about its driver layout you think makes it promising...

I actually don't see much of an advantage if any at all. I always end up crossing my speakers over higher than that and never hear a reall loss in localization or imaging. The only advantage I see is not having to but a stand that will not be as good as a tower speaker. Theoretically, there is an advantage, but in practice it's not a big one.

Makes sense. No fiddling is best, in that case JBL LSR305/Studio 230 and Kef Q300 are best. Later , as I mentioned earlier, i will look at adding 2 nearfield subs for KEFs as they will benefit a lot from highish crossover. For JBLs a single sub,upto 80 Hz, should be enough.

Btw I was comparing the relatively small NHT classic 3 3-way bookshelfs with some of the best of the KEFs and they seem quite good horizontally.Seems to have wider dispersion than KEFs, though its vertical is obviously not as good, but should be enough ?A foam "moustache" is also included to address dips in tweeter response at around 7kHz

Btw, just to confirm , you see any issues with vertical polar of classic 3s ? ( there stereophile review has it)

About HT setup ? I am just confused as to what db level should one shoot for ? Ref level just sounds too much to me [ pun intended :) ]. In my living room (22’L x 14’W x 10’H) at a distance of 6ft from spks, even 80 was loud to me, 105 peak will be just too much, eve if transients (probably no issues in dedicated and treated HT room). The SPL target dictates the speaker sizes to be used, esp to keep it discreet in the living room as well have smaller speakers behind an AT screen.Though for subs, shooting for bit more would be needed to compensate for equal loudness contourI am wondering if 5” 2way is enough for side and surrounds and 6-8” 2 way for LCR (say classic 3 though its low sensitivity is not beneficial here)